tommath/bn_mp_cnt_lsb.c
Steffen Jaeckel 4e3f1344a5 provide tommath_private.h
tommath.h contains declarations for the public part of the library.
tommath_private.h contains the functions which are private to ltm and
should not be exposed to the public.
2015-11-12 01:49:07 +01:00

54 lines
1.2 KiB
C

#include <tommath_private.h>
#ifdef BN_MP_CNT_LSB_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis
*
* LibTomMath is a library that provides multiple-precision
* integer arithmetic as well as number theoretic functionality.
*
* The library was designed directly after the MPI library by
* Michael Fromberger but has been written from scratch with
* additional optimizations in place.
*
* The library is free for all purposes without any express
* guarantee it works.
*
* Tom St Denis, tstdenis82@gmail.com, http://libtom.org
*/
static const int lnz[16] = {
4, 0, 1, 0, 2, 0, 1, 0, 3, 0, 1, 0, 2, 0, 1, 0
};
/* Counts the number of lsbs which are zero before the first zero bit */
int mp_cnt_lsb(mp_int *a)
{
int x;
mp_digit q, qq;
/* easy out */
if (mp_iszero(a) == MP_YES) {
return 0;
}
/* scan lower digits until non-zero */
for (x = 0; x < a->used && a->dp[x] == 0; x++) {}
q = a->dp[x];
x *= DIGIT_BIT;
/* now scan this digit until a 1 is found */
if ((q & 1) == 0) {
do {
qq = q & 15;
x += lnz[qq];
q >>= 4;
} while (qq == 0);
}
return x;
}
#endif
/* $Source$ */
/* $Revision$ */
/* $Date$ */